The problem is companding (TX compression - RX expansion) - that's the advantage of the Line 6, its signal chain is basically straight into a 24bit A/D with no companding. Delays in the measurement system are easily accounted for.

The problem is companding (TX compression - RX expansion) - that's the advantage of the Line 6, its signal chain is basically straight into a 24bit A/D with no companding. Delays in the measurement system are easily accounted for.

Digital systems that use data compression will also be problematic. Some do, some donít.

Don is exactly right. Digital wireless is no guarantee of the absence of artifacts that can make the system unusable for measurement applications. Iíve found that wireless systems of any type that are capable of fairly high channel counts generally cannot be used as a mic cable replacement for acoustic measurement. The Lectrosonics Hybrid system is a rare exception.

I recently tried a MIPRO ACT-818 receiver with TA-80 plug-on transmitter. It is a digital system that is advertised "to eliminate compander noise" and to be suitable for "acoustical measurements". I beg to differ. :)

Measurements

I set the TA-80 transmitter to its 24dB gain setting (reasonable for many measurement mics) and found the 1kHz clipping/limiting threshold and made log swept sine and Maximum Length Sequence (MLS) measurements 1dB below that threshold. Then I repeated those measurements 20dB below that threshold. I included MLS measurements because that process is extremely sensitive to non-linearities and time variance (LTI violations). Swept sines are the most forgiving of the non-LTI behavior present in almost all real acoustic systems to some extent. MLS freaks out if LTI is violated even slightly and makes a great blood hound when youíre looking for imperfections. Green and pink traces are MLS.

I made the same tests on the Line 6 XD-V75 receiver with TBP12 beltpack transmitter. The cable for the beltpack: XLF pin 2 to TA4F pins 3-4. XLF pins 1-3 to TA4F pin 1. TA4F pin 2 unconnected. The big downside is no phantom power like the MIPRO plug-on has. Green and blue traces are MLS.